Thin-walled cellular or honeycomb structures of brittle materials are desirable for many uses and in particular for uses involving flow of hot fluids through such structures. Currently prominent among such uses are those wherein these structures serve as catalyst supports and heat exchange media mounted in casings or housings. Commonly these structures are fabricated of ceramic or glass-ceramic materials, although any of a great variety of other brittle materials (e.g. glass, cermet or brittle metal materials) could be employed as desired if they provided compatible properties (e.g. refractoriness, strength, chemical resistance, abrasion resistance, etc.) for the particular service conditions involved. Fabrication has been particularly convenient by firing the particulate form of such materials into their sintered materials form. The thin walls can usually vary in thickness from about 0.002 inch to about 0.050 inch and in porosity volume up to 50% or so. Cell densities can vary between about 20-900 cells/square inch of transverse cross-sectional area. It has been especially desirable for obtainng low back pressure effect to select wall thicknesses and cell densities to provide open frontal area of about 75% or greater.
One of the serious problems encountered with the varying flow of hot fluids through these thin-walled honeycomb structures in their breakage resulting from the thermal shock of extreme temperature variations over relatively short distances within these structures. In fact, such thermal shock breakage may result from nonuniform heating and/or cooling of the structures by any means. Often, this problem is minimized or avoided by fabricating the structures of a material having a very low coefficient of thermal expansion and/or with porosity and/or microcracks in the crystal structure thereof. However, it is not always possible to employ a material with an adequate degree of these thermal-shock-resistant features because of the service requirements for other properties (such as refractoriness) and/or because of the severity of thermal shock to be withstood.
Alternative or supplementary techniques previously proposed for enhancing thermal shock resistance of the thin-walled honeycomb structures have involved various structural modifications or cell configurations. U.S. Pat. No. 3,887,741 discloses employment of grooves in the periphery of the structures. U.S. Pat. No. 3,983,283 proposed making the structures with some discontinuities in the cell walls. Commonly assigned copending application Ser. No. 672,155, filed Mar. 31, 1976 by S. T. Gulati, shows structures with convexly and concavely curved (or "wiggly") walls. The above-noted application Ser. No. 711,987 teaches forming the structures with cross-sectional cell configurations that are T-shape, L-shape, cruciform, Z-shape and bow tie shape.